Results of a randomized study of the JAK inhibitor ruxolitinib (INC424) versus best available therapy (BAT) in primary myelofibrosis (PMF), post-polycythemia vera-myelofibrosis (PPV-MF) or post-essential thrombocythemia-myelofibrosis (PET-MF).

LBA6501 Background: MF, a myeloproliferative neoplasm characterized by dysregulation of the JAK pathway, is associated with splenomegaly, constitutional symptoms and reduced lifespan. Ruxolitinib is a potent and selective JAK1 and JAK2 inhibitor. Methods: COMFORT-II, a randomized (2:1) phase III study, compared the efficacy and safety of ruxolitinib PO BID with BAT (other agents or no therapy) in adults with intermediate-2 or high-risk (Cervantes et al, Blood 2009) PMF, PPV-MF or PET-MF and palpable splenomegaly. The primary endpoint was the proportion of patients (pts), stratified by baseline risk category, achieving ≥ 35% reduction in spleen volume at week (wk) 48 determined by MRI or CT. The key secondary endpoint was the proportion achieving ≥ 35% reduction in spleen volume at wk 24. Results: 219 pts were randomized: 146 to ruxolitinib and 73 to BAT. Both arms included 49% high- and 51% intermediate-2 risk pts. The wk 48 response rate was 28.5% vs 0% (ruxolitinib vs BAT, P 20%) adverse events (AEs) of any grade were (ruxolitinib vs BAT) thrombocytopenia (44.5% vs 9.6%), anemia (40.4% vs 12.3%), diarrhea (24.0% vs 11.0%), and peripheral edema (21.9% vs 26.0%). Grade 3-4 AEs occurring in ≥ 5% of pts in the ruxolitinib arm were: anemia (11%) and thrombocytopenia (7.5%). The most frequent grade 3-4 AEs in the BAT arm were anemia, thrombocytopenia, pneumonia and dyspnea (each 4.1%). Seven deaths occurred on treatment or within 28 days after end of treatment: 4 (2.7%) ruxolitinib and 3 (4.1%) BAT. Disposition of discontinuations were (ruxolitinib vs BAT) 8.2% vs 5.5% due to AEs and 1.4% vs 12.3% due to withdrawn consent. Conclusions: The COMFORT-II study demonstrates that ruxolitinib provides marked and sustained clinical benefit in spleen size and an acceptable safety profile relative to BAT, extends the positive results of COMFORT-I which compared ruxolitinib with placebo, and may result in a new standard of care for a large number of patients with MF.